There is a need in the polymers industry for a propylene-based polymer, which has both amorphous and elastomeric character. Such a product would have the novel combination of both high impact strength and high elasticity, in addition to the other properties associated with propylene-based polymers such as a relatively high melting point, low density and low crystallinity.
Stuart (U.S. Pat. No. 4,826,939) discloses a highly amorphous propylene-based olefin terpolymer made by a process wherein ethylene is very randomly incorporated into a chain along with propylene and hexene. The amorphous terpolymer of Stuart is very tacky and pressure sensitive, having a ring and ball softening point of about 75 to 120.degree. C. The process of making the disclosed amorphous terpolymer comprises polymerizing the monomers in the presence of a traditional anionic coordination catalyst within a temperature range typical of a solution polymerization processes, about 140 to 250.degree. C. These materials are not elastic.
Collette (U.S. Pat. No. 4,335,225) discloses that a semicrystalline or crystalline block polypropylene having excellent elastomeric properties can be made with the use of particular titanium, zirconium, or halfnium-based catalyst systems at very low yield in a slurry process. The use of these exotic catalysts requires very mild processing conditions because the catalysts are particularly sensitive to air, heat, and light. They are not suitable or readily adaptable to a solution process.
In light of the above, it would be desirable to provide an amorphous propylene-based olefin terpolymer which is elastomeric instead of tacky. It would be further desirable for such terpolymer to be produced via an economical process that does not require an exotic or unusually temperamental catalyst system.